1. Scope of the Invention
This invention relates to the perimeter security and surveillance field, and more particularly to the use of fiber optic bundles for protecting the perimeter of an extended area precinct by detecting traverse of the perimeter by an intruder and localizing the point at which the perimeter was traversed.
2. Description of the Prior Art
There is a need to provide an economic means to protect literally miles of a preferred perimeter against unauthorized intruders under all conditions. A number of perimeter protection schemes have aimed to accomplish this. These schemes include the use X-band line-of-sight radar beams, free space infrared surveillance equipment, and buried leaky wave coaxial cables.
These systems have known limitations. For example, radar and free-space infrared systems are limited in their reliability and range by beam spreading, sidelobes, and variable attenuation due to weather conditions. Leaky wave systems are severely range limited (hundreds of feet) and are costly to install and maintain.
These limitations are overcome by fiber optic sensors which can be deployed over several miles and are also immune from electromagnetic interference (EMI) electromagnetic pulses (EMP).
Fiber optic sensor technology is described in an Optical Engineering/March/April 1985/Vol. 24 No. 2 article by Charles M. Davis entitled "Fiber optic sensors: an overview". The optic sensors in the article depend on the creation of sufficient distortion of the fiber to give rise to a dependably detectable reflection; or a sufficient distortion of the fiber to cause a dependably detectable change in transmission amplitude (power). These schemes utilize special localized (periodically repeated) sensor components or periodically repeated special sensitizing features, such as microbend deformers. Alternatively the fiber may be terminated in a mirror and interference between the incident and reflected wave detected. Such interferometer-detector arrangements are extremely delicate and prone to false alarms.
U.S. Pat. No. 4,696,889 discloses a method and apparatus wherein the exiting light from the trunk of a fiber optic assembly is projected onto a single photosensitive surface.